Various types of rotary feeders are known in the art for differing applications. When used in vacuum applications, for permitting ingress and egress of goods from a vacuum or pressure chamber, conventional rotary feeders comprise a circumferential seal which, in the case of a vacuum chamber is designed to minimize the leakage of air into the vacuum, and in the case of a pressure chamber is designed to minimize leakage of chamber gas out into the atmosphere.
Such seals are extremely cumbersome and expensive and involve significant frictional drag on the moving parts, and therefore require frequent and extensive maintenance. The high frictional drag on the moving parts also generates a need for more powerful vacuum pumps in the case of a vacuum chamber, and involves a considerable loss of gas in the case of a pressure chamber.
The use of a rotary feeder of the above general type in the context of a vacuum system having a sealing sleeve filled with a condensible gas is described in Israel Patent No. 50398, published Oct. 31, 1978, of the present inventor, and which corresponds to U.S. patent application Ser. No. 723,629, filed Sept. 15, 1976, now abandoned.
There is described and claimed in U.S. patent application Ser. No. 686,403, now abandoned, a rotary feeder comprising an enclosure defining an inlet and an outlet, a rotary feed member of generally cylindrical configuration arranged for rotation about its axis of symmetry within the housing and sealing apparatus arranged for sealing engagement with the rotary feed member at a location within the enclosure corresponding to either or both of the inlet and outlet, whereby frictional engagement of the rotary feed member with the sealing apparatus occurs only in the vicinity of either or both of the inlet and outlet and not throughout the enclosure or circumferentially of the rotary feed member.
In the apparatus described in the aforesaid U.S. patent application, Ser. No. 696,403, the sealing apparatus may be provided only at the outlet of the enclosure, only at the inlet of the enclosure, or at both the inlet and outlet of the enclosure.
A known application of vacuum chambers in the treatment of goods is that of the batch fumigation of nuts prior to marketing. It involves the provision of a vacuum chamber in which a batch of nuts is placed, and a high negative pressure is then applied inside the chamber for exhausting air from the space inside the nuts, between the meat of the nut and the nut shell.
Once the air has been exhausted from the nuts, the vacuum is then broken and a fumigant is introduced into the chamber which is allowed to diffuse and to be drawn into the nuts. The fumigant-laden nuts are allowed to sit for a relatively short period, of typically about three hours. A vacuum is then applied to the nuts in order to exhaust the fumigant therefrom, after which the nuts are removed from the chamber and a fresh batch of nuts is placed therein.
There are a number of disadvantages to the above described method for fumigation of nuts. One disadvantage is that a single batch of fumigant-laden nuts occupies the chamber for a period of several hours, thereby bringing the treatment plant to a standstill.
Additionally, there is a need to ensure that the nuts only occupy the chamber for the minimum allowable period of time, but ideally, they should be allowed to sit for as long as it takes for the fumigant gas to complete its fumigating action on the nuts and disintegrate. Such a length of time is normally far longer than the three hours allowed in the batch process outlined above.
An alternative nut treatment method involves exposing large batches of nuts to a fumigant gas at atmospheric pressure for a long period of time, about twenty four hours. This inevitably leads to non-uniform distribution of the gas amongst the nuts, some nuts being exposed to a smaller concentration of gas than is required, while others are exposed to a dangerously high concentration of gas. After the fumigation is completed, the chamber, or other enclosure, in which the fumigation has taken place, is aired, also for a period of about twenty four hours.
In both of the above-described fumigation processes, the vacuum chamber or other enclosure is flushed. This is not only wasteful of material, but can also lead to extensive air pollution.